Transient up-regulation of the rostrocaudal gradient of ephrin A2 in the tectum coincides with reestablishment of orderly projections during optic nerve regeneration in goldfish

During development, a graded expression of ephrin A2 has been implicated in retinotectal map formation. Here we have examined ephrin A2 expression dur ing optic nerve regeneration in the mature goldfish. In the tecta of normal animals, a gradient of ephrin A2 expression is detected in cell bodies wit hin the stratum fibrosum et griseum superficiale with more immunopositive c ells caudally than rostrally. The gradient in the mature animal presumably reflects the plasticity associated with continued retinal and tectal neurog enesis, During optic nerve regeneration, expression throughout the tectum i s increased by 1 month as a strong rostrocaudal gradient. The gradient decl ines to normal by 3 months. The up-regulation of ephrin A2 during optic ner ve regeneration is likely to be instrumental in reestablishing the retinote ctal map. (C) 2000 Academic Press.